Hdavidh/update javadocs tm copy object (#3831)

* Update Transfer Manager copyObject javadocs

* Update Transfer Manager copyObject javadocs

* Remove unused import - fix Checkstyle error

Author: davidh44

services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/S3TransferManager.java

@@ -15,7 +15,6 @@
 
 package software.amazon.awssdk.transfer.s3;
 
-import java.util.Map;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Executor;
 import java.util.function.Consumer;
@@ -614,11 +613,12 @@ default DirectoryDownload downloadDirectory(Consumer<DownloadDirectoryRequest.Bu
     /**
      * Creates a copy of an object that is already stored in S3 in the same region.
      * <p>
-     * Under the hood, {@link S3TransferManager} will intelligently use plain {@link CopyObjectRequest}s for smaller objects, or
-     * multiple parallel {@link UploadPartCopyRequest}s for larger objects. This behavior can be configured via
+     * Depending on the underlying S3Client, {@link S3TransferManager} may intelligently use plain {@link CopyObjectRequest}s
+     * for smaller objects, and multiple parallel {@link UploadPartCopyRequest}s for larger objects. If multipart copy is
+     * supported by the underlying S3Client, this behavior can be configured via
      * {@link S3CrtAsyncClientBuilder#minimumPartSizeInBytes(Long)}. Note that for multipart copy request, existing metadata
-     * stored in the source object is NOT copied to the destination object; if required, you can retrieve the metadata
-     * from the source object and set it explicitly in the {@link CopyObjectRequest.Builder#metadata(Map)}.
+     * stored in the source object is NOT copied to the destination object; if required, you can retrieve the metadata from the
+     * source object and set it explicitly in the @link CopyObjectRequest.Builder#metadata(Map)}.
      *
      * <p>
      * While this API supports {@link TransferListener}s, they will not receive {@code bytesTransferred} callback-updates due to